JP2015014577A - Electromagnetic flowmeter and insulation deterioration diagnostic method of exciting coil in electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic flowmeter in which insulation deterioration of an exciting coil can be diagnosed using a circuit for flow measurement.SOLUTION: The electromagnetic flowmeter measures flow rate of a liquid to be measured by applying exciting current with a predetermined waveform to an exciting coil, and obtains a flow rate signal which is based on electromotive force of the liquid to be measured flowing in a measurement pipe. The electromagnetic flowmeter includes: a detection resistance for detecting the exciting current; an exciting part for controlling pulse width in on-time based on a detection result of the exciting current and generating the exciting current with the predetermined waveform by switching operation in which the minimum value of the pulse width is provided; and a diagnostic part for diagnosing insulation deterioration of the exciting coil based on the detected exciting current value.

Description

  The present invention relates to an electromagnetic flowmeter that measures a flow rate of a fluid to be measured by applying a magnetic field to a fluid to be measured flowing in a measurement tube and measuring an electromotive force, and an insulation deterioration diagnosis method for an excitation coil in the electromagnetic flowmeter.

  2. Description of the Related Art An electromagnetic flow meter that measures the flow rate of a conductive fluid using electromagnetic induction is known. The electromagnetic flowmeter measures a generated electromotive force using a pair of detection electrodes attached in the measurement tube by flowing a fluid to be measured in the measurement tube to which a magnetic field is applied in an orthogonal direction. Since this electromotive force is proportional to the flow velocity of the fluid to be measured, the volume flow rate of the fluid to be measured can be obtained based on the measured value.

  FIG. 7 is a diagram showing a configuration of a conventional electromagnetic flow meter 400. In the example of this figure, the electromagnetic flowmeter 400 shall measure the flow volume of the electroconductive fluid to be measured which flows through the measuring tube 500.

  An electrode A 410 a and an electrode B 410 b are attached to the measurement tube 500 as detection electrodes, and an exciting coil 411 is disposed in the vicinity of the outside of the measurement tube 500. The exciting coil 411 generates a magnetic field by the exciting current output from the exciting unit 440. The magnetic field generated by the excitation coil 411, the electromotive force detection direction of the electrode A 410a and the electrode B 410b, and the flow direction of the measurement tube 500 are configured to be orthogonal to each other.

  The excitation current output from the excitation unit 440 superimposes a short-cycle pulse and a long-cycle pulse as shown in FIG. 8A in order to stabilize the zero point and improve noise resistance and high-speed response. A two-frequency excitation waveform having a positive excitation period and a negative excitation period is used. However, it may be a single frequency excitation waveform or other excitation waveform.

  The excitation unit 440 includes a current control unit 441, a switching unit 442, and a power source 443. Under the control of the excitation control unit 431 of the control unit 430, positive / negative control and PWM control are performed on the power supplied from the power source 443. The above-described two-frequency excitation waveform is output. In the PWM control, the current control unit 441 detects the exciting current using the current detection resistor Rd and controls the operation of the switching unit 442 so as to obtain a predetermined current value. For this reason, as shown in the enlarged view of the excitation waveform in FIG. 8B, the excitation waveform contains a ripple component corresponding to the switching operation.

  The electromotive force generated in the measurement tube 500 by the magnetic field generated by the excitation coil 411 is detected by the electrode A 410a and the electrode B 410b, input to the differential amplifier 420 via a buffer (not shown), and the difference is taken out as a flow signal.

  The flow rate signal output from the differential amplifier 420 is digitally converted by an A / D converter (not shown). And it inputs into the flow volume calculating part 432 of the control part 430, and the flow volume of to-be-measured fluid is calculated based on a flow signal.

JP 2008-20364 A JP 2003-106879 A

  In the electromagnetic flow meter 400, the insulation between the lines of the exciting coil 411 may deteriorate due to, for example, the fluid under measurement entering the exciting coil 411 due to aging deterioration of the seal member of the measuring tube 500 or the like.

  If the insulation between the lines of the exciting coil 411 deteriorates, the generated magnetic field may change, affecting flow rate measurement, or making measurement impossible. For this reason, for example, it has been conventionally proposed to provide an insulation resistance diagnosis unit 450 and diagnose the degree of deterioration of the insulation resistance of the exciting coil 411. As the insulation resistance diagnosis unit 450, a circuit that measures the inductance of the exciting coil 411 or a circuit that measures the resistance of the exciting coil 411 is used. This utilizes the characteristic that the inductance decreases as the insulation deterioration between the lines of the excitation coil 411 progresses, and the resistance value of the excitation coil 411 decreases as the insulation deterioration further progresses.

  In this way, it is possible to diagnose the degree of deterioration of the insulation resistance of the exciting coil 411 using a circuit that measures the inductance and resistance of the exciting coil 411. However, the measurement circuit for diagnosing insulation deterioration is a circuit for measuring flow rate. It must be provided separately from this, leading to an increase in cost. For this reason, it would be beneficial if the insulation deterioration of the coil could be diagnosed using the inherent flow measurement circuit.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make it possible to diagnose an insulation deterioration of a coil by using a flow measurement circuit in an electromagnetic flow meter.

In order to solve the above problems, an electromagnetic flow meter according to a first aspect of the present invention applies an excitation current having a predetermined waveform to an excitation coil, and acquires a flow signal based on an electromotive force of a fluid to be measured flowing in a measurement tube. An electromagnetic flow meter for measuring the flow rate of the fluid to be measured, the detection resistor for detecting the excitation current, and the pulse width at the on-time based on the detection result of the excitation current and the minimum value of the pulse width And an diagnosing unit for diagnosing insulation deterioration of the exciting coil based on the detected value of the exciting current.
Here, the diagnosis unit can determine that the insulation of the excitation coil has deteriorated when the detected value of the excitation current exceeds a reference value.
In addition, the minimum value of the pulse width can be set to a value that can supply the excitation coil with power larger than the power consumed by the excitation coil in the state of the excitation coil to be determined to be deteriorated.
In order to solve the above-described problem, an insulation deterioration diagnosis method for an exciting coil in an electromagnetic flowmeter according to a second aspect of the present invention is generated by a switching operation for controlling a pulse width at the time of ON based on a detection result of excitation current. Insulation deterioration of the excitation coil in an electromagnetic flowmeter that applies a predetermined waveform of excitation current to the excitation coil, obtains a flow rate signal based on the electromotive force of the fluid to be measured flowing in the measurement tube, and measures the flow rate of the fluid to be measured A diagnostic method is characterized in that a minimum value is provided for the pulse width, the excitation current is detected, and insulation deterioration of the excitation coil is diagnosed based on the detected value of the excitation current.

  According to the present invention, in an electromagnetic flow meter, it is possible to diagnose insulation deterioration of a coil by using a flow measurement circuit.

It is a block diagram which shows the structure of the electromagnetic flowmeter which concerns on this embodiment. It is a block diagram which shows the structure of an excitation part. It is a flowchart explaining operation | movement of a coil insulation deterioration diagnostic part. It is a figure explaining the increase of the minimum pulse width and exciting current. It is a figure explaining the relationship between the insulation deterioration of an exciting coil, and the amount of ripples. It is a figure which shows the example of output control of the multistep alarm of a coil insulation deterioration diagnostic part. It is a block diagram which shows the structure of the conventional electromagnetic flowmeter. It is a figure explaining an excitation waveform.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an electromagnetic flow meter 100 according to the present embodiment. As shown in the figure, the electromagnetic flow meter 100 includes an electrode A 110 a, an electrode B 110 b, an excitation coil 111, a current detection resistor Rd, a differential amplifier 120, a control unit 130, and an excitation unit 140, and flows through the measurement tube 500. Measure the flow rate of the conductive fluid to be measured. The control unit 130 can be configured using an arithmetic processing device such as a CPU.

  The electrode A 110 a and the electrode B 110 b are attached to the measurement tube 500 as detection electrodes, and the excitation coil 111 is disposed in the vicinity outside the measurement tube 500. The exciting coil 111 generates a magnetic field by the exciting current output from the exciting unit 140. The magnetic field generated by the exciting coil 111, the electromotive force detection direction of the electrode A110a and the electrode B110b, and the flow path direction of the measuring tube 500 are configured to be orthogonal to each other.

  The excitation current output from the excitation unit 140 is a current having a positive excitation period and a negative excitation period as in the conventional case, and has a two-frequency excitation waveform in which a short-cycle pulse and a long-cycle pulse are superimposed.

Excitation portion 140, the current control unit 141, switching unit 142 includes a power supply 143 for outputting a constant voltage _{V EX,} under the control of the excitation control unit 131 of the control unit 130, the positive and negative power supplies power 143 By performing control and PWM control, a two-frequency excitation waveform is output. However, it may be a single frequency excitation waveform or other excitation waveform.

  FIG. 2 is a block diagram showing a configuration of the excitation unit 140. As shown in the figure, the current control unit 141 detects the excitation current based on the voltage drop generated in the current detection resistor Rd, and outputs a difference from the set current value. At this time, the sign of the excitation current is taken into consideration. The PWM control unit 145 controls the pulse width of the continuous pulse to be output based on this difference. That is, control is performed so that the exciting current becomes a set current value by a feedback operation. In the present embodiment, the PWM control unit 145 includes a minimum pulse width limiting unit 146 in order to cause the excitation current to exceed the set current value when the insulation deterioration of the excitation coil 111 proceeds. . The operation of the minimum pulse width limiting unit 146 will be described later.

  The switching unit 142 includes four switches for generating positive and negative excitation currents. In this example, the four switches are divided into two groups, and one group of switches is on / off controlled according to the excitation waveform, The series of switches are controlled to be turned on and off according to the AND of the excitation waveform and the PWM-controlled pulse. However, other switching control may be used. For example, the excitation waveform and the PWM-controlled pulse may be controlled on and off with separate switches.

  Returning to the description of FIG. 1, the electromotive force generated in the measurement tube 500 by the magnetic field generated by the exciting coil 111 is detected by the electrode A 110a and the electrode B 110b, and is input to the differential amplifier 120 via a buffer (not shown). The difference is extracted as a flow signal.

  The flow rate signal output from the differential amplifier 120 is digitally converted by an A / D converter (not shown). And it inputs into the flow volume calculating part 132 of the control part 130, and the flow volume of the to-be-measured fluid is calculated based on a flow signal.

  The electromagnetic flow meter 100 according to the present embodiment includes a coil insulation deterioration diagnosis unit 133 in the control unit 130. The coil insulation deterioration diagnosis unit 133 cooperates with the minimum pulse width restriction unit 146 of the PWM control unit 145 to diagnose insulation deterioration of the exciting coil 111 based on the current detected by the current detection resistor Rd. Since the current detection resistor Rd is conventionally provided for detecting the excitation current, it is not necessary to separately provide a measurement circuit for diagnosing insulation deterioration of the excitation coil 111.

  FIG. 3 is a flowchart for explaining the operation of the coil insulation deterioration diagnosis unit 133. This operation may be performed constantly during operation of the electromagnetic flow meter 100, or may be performed at predetermined intervals, or may be performed in response to an instruction or activation from the user.

  First, an excitation current during a period in which a pulse is generated is detected based on a voltage drop generated in the current detection resistor Rd (S101). Then, the current value is measured (S102).

Here, the relationship between the insulation deterioration of the exciting coil 111 and the exciting current value will be described. Generally, the exciting coil 111 has a characteristic that the resistance value decreases as the insulation deterioration proceeds. Since the output voltage of the power supply 143 is constant at _VEX , when the resistance value of the excitation coil 111 decreases, the power consumed by the excitation coil 111 decreases.

  As described above, the PWM control unit 145 controls the switching operation of the switching unit 142 so that the current value detected by the current detection unit 144 becomes a predetermined current value. Specifically, if the detected current is smaller than a predetermined current value, the pulse width is made longer, and if the detected current is larger than the predetermined current value, the pulse width is made shorter. For example, when the switching operation is performed with the pulse width as shown in FIG. 4A, if the detected current value increases, the pulse width is shortened as shown in FIG. Suppresses the rise.

  However, in the present embodiment, the minimum pulse width limiting unit 146 of the PWM control unit 145 has a pulse width larger than a preset minimum pulse width even when the detected current is larger than a predetermined current value. Limit so as not to shorten.

  Here, the minimum pulse width is a width that allows the necessary power to be supplied to the exciting coil 111 at normal times when the exciting coil 111 is not deteriorated in insulation. The minimum pulse width is smaller than that when the deterioration of insulation progresses and the power consumption decreases. The width is sufficient to supply a large amount of power.

  That is, since the pulse width is sufficiently longer than the minimum pulse width at normal times, the power consumption in the excitation coil 111 and the power supplied from the excitation unit 140 are substantially equal without being affected by the minimum pulse width. On the other hand, in the state where the insulation deterioration has progressed, the pulse width becomes the minimum pulse width, and the power supplied from the excitation unit 140 is larger than the power consumption in the excitation coil 111.

  As a result, in the state where the insulation deterioration has progressed, as shown in FIG. 4C, the exciting current increases without being constant and becomes larger than a predetermined current value. For this reason, the coil insulation deterioration diagnosis unit 133 can detect that the insulation deterioration has progressed by measuring the excitation current and detecting that it has become higher than the reference current value.

  Returning to the description of the flowchart of FIG. 3, the coil insulation deterioration diagnosis unit 133 determines whether or not the measured current value exceeds a preset reference value (S103). The information is output to notify the user that the insulation of the exciting coil 111 has deteriorated (S104). At this time, in order to avoid misdiagnosis, an alarm may be output when the state where the measured current value exceeds the reference value continues.

  By the way, the exciting coil 111 also has a characteristic that the inductance decreases when the insulation deteriorates. Using this characteristic, a plurality of levels of alarms may be output. In this case, for example, a preliminary alarm is generated based on a decrease in inductance to notify that the insulation of the excitation coil 111 has deteriorated, and this alarm is generated based on an increase in excitation current due to the above-described minimum pulse width limitation. By doing so, it can be notified that the insulation of the exciting coil 111 is further deteriorated.

  An alarm generation procedure based on a decrease in inductance will be described. First, an excitation current during a period in which a pulse is generated is detected based on a voltage drop generated in the current detection resistor Rd. As described above, since this exciting current is controlled to have a predetermined value by the switching operation, it contains a ripple component.

  The coil insulation deterioration diagnosis unit 133 measures the amount of this ripple component. The amount of the ripple component can be represented by, for example, the absolute value of the difference between the maximum value and the minimum value of the excitation current in the pulse generation period, the ratio to the pulse height, and the like. At this time, it is desirable to perform processing for removing the influence of noise and the like.

Here, the relationship between the insulation deterioration of the exciting coil 111 and the ripple amount will be described. As described above, when the insulation of the exciting coil 111 deteriorates, the inductance L of the exciting coil 111 decreases. Assuming that the exciting current is i, the output voltage of the power supply 143 is constant at V _EX . Therefore, from [Equation 1], when the inductance L is reduced, di that is a fluctuation amount of the exciting current is increased. For this reason, as shown in FIG. 5, when the insulation of the exciting coil 111 deteriorates, the ripple amount increases.
Therefore, the coil insulation deterioration diagnosis unit 133 determines whether or not the measured ripple amount exceeds a preset reference value, and if so, outputs an alarm and the insulation of the excitation coil 111 deteriorates. To the user. At this time, an alarm may be output when the state where the ripple amount exceeds the reference value continues to avoid erroneous diagnosis. Further, when the detected excitation current is small, the determination may be made based on a signal amplified using an amplifier.

  Note that when the ripple amount of the excitation current increases, the ripple component included in the voltage detected by the electrode 110 also increases. The insulation deterioration of the exciting coil 111 may be determined by evaluating the amount of the ripple component or the ripple component included in the flow rate signal input to the flow rate calculation unit 132.

  The coil insulation deterioration diagnosis unit 133 can perform, for example, a plurality of stages of alarm output control as shown in FIG. 6 by using the above two types of diagnosis methods in combination. When insulation deterioration of the exciting coil 111 proceeds from a normal state, the inductance of the exciting coil 111 decreases and the ripple amount increases as shown in FIG. Therefore, a preliminary alarm is generated when the ripple amount exceeds the ripple amount reference value. The ripple amount reference value for generating the preliminary alarm is made to correspond to the degree of insulation deterioration that does not affect the measurement result.

  Further, as the insulation deterioration progresses, as shown in FIG. 6B, the resistance value of the exciting coil 111 decreases and the pulse width decreases. When the pulse width is reduced to the minimum pulse width, the excitation current increases. Therefore, this alarm is generated when the excitation current exceeds the excitation current reference value. The excitation current reference value for generating this alarm is made to correspond to the degree of insulation deterioration that may affect the measurement result when the insulation deterioration further proceeds. Further, an intermediate alarm may be generated when the pulse width reaches the minimum pulse width.

  As described above, according to the electromagnetic flow meter of the present embodiment, since the insulation deterioration of the excitation coil 111 is diagnosed based on the excitation current, the insulation deterioration of the coil can be diagnosed using the flow measurement circuit. Become. Further, by adopting a plurality of diagnostic methods, it becomes possible to perform a plurality of steps of alarm output control.

DESCRIPTION OF SYMBOLS 100 ... Electromagnetic flowmeter, 110 ... Electrode, 111 ... Excitation coil, 120 ... Differential amplifier, 130 ... Control part, 131 ... Excitation control part, 132 ... Flow rate calculation part, 133 ... Coil insulation deterioration diagnostic part, 140 ... Excitation part , 141 ... current control unit, 142 ... switching unit, 143 ... power supply, 144 ... current detection unit, 145 ... PWM control unit, 146 ... minimum pulse width limiting unit, 400 ... electromagnetic flow meter, 411 ... excitation coil, 420 ... difference Dynamic amplifier, 430 ... control unit, 431 ... excitation control unit, 432 ... flow rate calculation unit, 440 ... excitation unit, 441 ... current control unit, 442 ... switching unit, 443 ... power source, 450 ... insulation resistance diagnostic unit, 500 ... measurement tube

Claims (4)

An electromagnetic flowmeter that applies an excitation current having a predetermined waveform to an excitation coil, acquires a flow rate signal based on an electromotive force of a fluid to be measured flowing in a measurement tube, and measures the flow rate of the fluid to be measured,
A detection resistor for detecting the excitation current;
An excitation unit that controls the pulse width at the time of ON based on the detection result of the excitation current and generates the excitation current of the predetermined waveform by a switching operation provided with a minimum value of the pulse width;
An electromagnetic flowmeter comprising: a diagnosis unit that diagnoses insulation deterioration of the excitation coil based on the detected value of the excitation current.   The electromagnetic flowmeter according to claim 1, wherein the diagnosis unit determines that the insulation of the excitation coil has deteriorated when the detected value of the excitation current exceeds a reference value.   2. The minimum value of the pulse width is a value that can supply electric power larger than electric power consumed by the exciting coil in the state of the exciting coil to be determined to be deteriorated. Or the electromagnetic flowmeter of 2. Apply an excitation current with a predetermined waveform generated by a switching operation that controls the pulse width at ON based on the detection result of the excitation current to the excitation coil, and obtain a flow signal based on the electromotive force of the fluid to be measured flowing in the measurement tube An insulation deterioration diagnosis method for the exciting coil in an electromagnetic flowmeter that measures the flow rate of the fluid to be measured,
An insulation deterioration diagnosis method comprising: providing a minimum value for the pulse width; detecting the excitation current; and diagnosing insulation deterioration of the excitation coil based on the detected value of the excitation current.